Room-temperature synthesis of yellow TiO2 nanoparticles with enhanced photocatalytic properties

Anatase titanium dioxide (TiO₂) nanoparticles have been successfully synthesized through a simple approach at low temperature. Particularly yellow TiO₂ is well obtained at room temperature (25 °C). TiO₂ samples are characterized by XRD, Raman, XPS, TEM, BET, UV-Vis, and Zeta Potential. The zeta potential value of TiO₂ samples can be tuned from -26.8 to +13.6 mV by different reaction temperature. The yellow TiO₂ has more oxygen vacancies and Ti³⁺ compared with other samples, which reduces the band gap from 3.1 to 2.9 eV and made the conduction band positively shift about 0.2 eV. Electrochemical impedance spectroscopy and Mott-Schottky plots reveal that the yellow TiO₂ nanocrystals had higher carrier density and better conductivity for electron transfer. According to the XPS analysis, the Ti³⁺ content in different samples is 8.1%, 7.8%, 6%, 1%, and zero, respectively. The decomposition rate of Rhodamine B under UV light and visible light was 99.7% and 70.0%, and the NO removal efficiency in 5 min is 84.8% for yellow TiO₂, respectively. The enhanced photocatalytic performance can be attributed to the presence of more oxygen vacancies in yellow TiO₂ that can act as traps to reduce the recombination of e^-/h⁺ pairs.